1. Field of the Invention
The present invention relates to a wiring structure of a magnetic head driving device in a storage apparatus.
2. Description of the Related Art
FIGS. 1A and 1B illustrate crosstalk in a magnetic head driving device of a related storage apparatus.
FIG. 1A is used to give a general description of crosstalk. The influence of crosstalk on a read head during writing will be described from a transmission path structure and a head 52 of a related magnetic head driving device 51.
During writing, electrical current of a write signal flows towards a coil of a write head from an LSI in a driving circuit 59 (preamplifier). At this time, since four wires comprising write wires and read wires must be disposed in a space, which is narrow in a thickness direction of a head arm, between the driving circuit 59 and the head 52, particularly, between the driving circuit 59 and a flexure, the distances between the write wires and the read wires must be small. Moreover, the use of a larger number of wires for other purposes is proposed. Therefore, the distances between the wires tend to become smaller.
Consequently, since the distances between the wires are small, crosstalk electrical current tends to be produced in the read wires due to coupling between the wires resulting from write electrical current flowing through the write wires.
When the wires are disposed between the head 52 and the flexure by using a flexible printed circuit board, the wires are disposed at the narrow flexure, thereby inevitably reducing the distances between the wires. Therefore, reducing the size of the flexure similarly tends to produce crosstalk electrical current.
From a different viewpoint, since, in the head 52, an MR element of the read head is disposed directly below a thin-film coil of the write head, crosstalk electrical current may flow directly to the MR element from the coil or an internal wire in the write head.
In addition, since the write signal of a few tens of mA is produced for writing data, electrical current of a few tens of mA may flow in the read wires due to crosstalk electrical current that is generated during writing. In contrast, an allowable current (withstand pressure) of the MR element is on the order of a few mA. Therefore, even if crosstalk electrical current has a value on the order of a few mA, the crosstalk electrical current has a great influence on the read wires.
In particular, if the crosstalk electrical current flows into the MR element, the MR element may deteriorate or break due to the quantity of electricity.
Further, the MR element is a tunneling magnetoresistive (TMR) element. Accordingly, the influence of crosstalk electrical current on the MR element due to a smaller allowable quantity of electricity of the MR element is an important problem.
FIG. 1B shows the transmission path structure. The transmission path from the preamplifier 59 to the head 52 is defined by disposing at an actuator the preamplifier 59, a read-write/flexible printed circuit board 58 (RW/FPC 58 in the figure), a relay-flexible-printed-circuit-board and read-write/flexible-printed-circuit-board connecting portion 57 (relay-FPC and RW/FPC connecting portion 57 in the figure), a relay flexible printed circuit board body 56 (relay FPC 56 in the figure), a flexure and relay-flexible-printed-circuit-board connecting portion 55 (flexure and relay-FPC connecting portion 55 in the figure), a flexure 54, and the head 52 formed on a slider 53. A relay flexible printed circuit board 60 comprises the flexure and relay-FPC connecting portion 55, the relay FPC body 56, and the flexure and relay-flexible-printed-circuit-board connecting portion 55.
In the related magnetic head driving device 51, when a write electrical current flows to the head 52 from the preamplifier 59, the flow of the electrical current influences a read wire rx disposed close to and parallel with a write wire wy, causing crosstalk electrical current to flow along the read wire rx as it is in the direction of the read head (as indicated by the broken arrow in FIG. 1B). As a result, a load that is equal to or greater than the withstand pressure is applied to the MR element of the read head. This may cause the MR element to break.
In addition, since the read MR element is disposed directly below the write coil, the write wire is closest to one of the poles of the read wire in the head 52. Therefore, a strong crosstalk electrical current is generated in the read wire disposed directly below the write wire. When the polarity of the crosstalk electrical current in the read head is the same as the polarity of the crosstalk between the wires in the transmission path, a larger stress is applied to the MR element due to a synergistic action.